[perf] pylint: Use multiple processes to speed up Pylint.

Specifying '-j 0' will auto-detect the number of processors available to use.

Suggested-by: @dalf / https://github.com/searx/searx/pull/2421#issuecomment-751444257


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>